1. Field of the Invention
The present invention relates to a hollow plate made of synthetic resin and used as the luggage panel, tonneau-board or the like which is arranged at the back of the rear seat in cars, for example.
2. Prior Art
Conventionally, the luggage panel for cars, for example, is made by blow-molding synthetic resin to a hollow plate which is light in weight and easy to manufacture.
FIG. 1 shows one of these conventional hollow plates wherein semi-melted hollow body (which will be hereinafter referred to as parison) of synthetic resin is placed in a die, deformed along the die by pressurized air blown in, and then cooled and hardened. The hollow plate thus formed has hollow portions (b) and its lower face (c) is corrugated to intermittently form together with its upper face (d) those portions (e) where the lower and upper faces are contacted each other. It is arranged that T equals to 2t by 0.8 wherein T represents the thickness of each of these contacted portions (e) and (t) denotes the thickness of each of the lower and upper faces (c) and (d). The lower and upper faces (c) and (d) are thus reliably contacted each other at these portions (e).
The hollow plate of this kind is provided with the contacted portions (e) to reinforce its rigidity, and it is often seen that some reinforcing members (f) such as pipes are inserted into its hollow portions to further enhance its rigidity. When the reinforcing members (f) are inserted at its molding process in this case, it is warped because of shrinkage difference between its resin and the reinforcing member (f). Therefore, each of the reinforcing members (f) has a diameter fitting to its respective hollow portion and they are inserted into the hollow portions after the molding process.
In the case of the hollow plate thus formed, however, its contacted portions (e) are compressed to have a thickness of T=2t.times.0.8. Therefore, this compression causes parison flashes to be swelled out, each having a mass of about 2t-T. The parison flashes are swelled out into the hollow portions to form protruded portions (g) in the hollow portions, as shown in FIG. 1. It is therefore often seen that the reinforcing members (f) each of which is selected to have a diameter fitting to its respective hollow portion cannot be inserted into the hollow portions (b) because of the protruded portions (g). Further, the protruded portions (g) thus formed are different in size. The reinforcing members (f) must be selected therefore to have diameters which are different every hollow portion. If not, they may not fit to the hollow portions, or they may crack or swell those resin portions where they are forcedly inserted.